The present invention relates generally to the field of solar thermal energy. In particular, the present invention relates to a manifold for a solar thermal energy collector.
Solar thermal energy collectors convert the energy of the sun into a more usable or storable form. Sunlight provides energy in the form of electromagnetic radiation from the infrared (long) to the ultraviolet (short) wavelengths. The intensity of solar energy striking the earth's surface at any one time depends on weather conditions. On a clear day measured on a surface directly perpendicular to the sun's rays solar energy averages about one thousand watts per square meter. The best designed solar collectors are the ones that collect the most sunlight and are therefore most efficient.
Solar thermal energy collectors can provide heat to hot water systems, swimming pools, floor-coil heating circuit and the like. They may also be used for heating an industrial dryer, providing input energy for a cooling system or providing steam for industrial applications. The heat is sometimes stored in insulated storage tanks full of water. Heat storage may cover a day or two day's requirements.
A solar thermal energy collector that stores heat energy is called a “batch” type system. Other types of solar thermal collectors do not store energy but instead use fluid circulation (usually water or an antifreeze solution) to transfer the heat for direct use or storage in an insulated reservoir. The direct radiation is usually captured using a dark colored surface which absorbs the radiation as heat and conducts it to the transfer fluid. Metal makes a good thermal conductor, especially copper and aluminum. In high performance collectors, a selective surface is used in which the energy collector surface is coated with a material having properties of high-absorption and low emission. The warmed fluid leaving the collector is either directly stored, or else passes through a heat exchanger to warm another tank of water, or is used to heat, for example a building, directly. The temperature differential across an efficient solar collector is typically only ten to twenty degrees centigrade.
Solar thermal energy collectors often include an array of solar collector tubes and a manifold. These systems may be supplied with water from a storage tank located below the collectors. The water is typically circulated by a pump. When the pump is not operating, the water drains from the collectors into the tank. Each solar thermal energy collector may include a housing, a collector panel within the housing and a cavity through which water is circulated with supply and drain pipes. The supply and drain pipes of some of the collectors may be connected to the manifold at bushings which fit into aligned ends of the pipes and fittings. The supply and drain pipes of collectors may also be plugged into the supply and drain pipes of other collectors which are along the manifold, again the connections being at bushing.
A solar thermal energy collector may be made of a series of modular collector tubes, mounted in parallel, whose number can be adjusted to meet requirements. This type of solar thermal energy collector usually consists of rows of parallel collector tubes. Types of tubes are distinguished by their heat transfer method. For example, a U-shaped copper tube may be used to transfer the fluid inside glass collector tubes. In another example, a sealed heat pipe may transfer heat from a collector tube to fluid flowing through the collector tube. For both examples, the heated liquid circulates through the manifold for use or storage. Water heated in such a manner may be stored where it is further warmed by ambient sunlight. Evacuated collector tubes heat to higher temperatures, with some models providing considerably more solar yield per square meter than flat panels.
An array of tube heat exchangers, also referred to as collector tubes, are often placed in a solar thermal panel for easy of transfer and installation. Such a panel may include tubes that are surrounded on each side by two deformed plates. These plates cover each tube and are secured together by rivets which are spaced along and traverse the deformed portions of the plates, thus providing a spring section to absorb unequal expansion of the plates and the fluid conducting pipes.
For efficiency, solar thermal energy collectors are designed to minimize resistance to fluid flow. A common inlet, or manifold, may be used to reduce the resistance to fluid flow, and thus to reduce pressure loss. Collector tubes are typically connected in series or parallel with manifolds made from additional lengths of tubing. These tubes are usually joined by soldering and brazing. Other methods for joining these tubes include coupling with grooves and recesses. Reducing pressure loss increases flow and therefore increases heat exchanged. Soldering and brazing are labor and time intensive techniques which are not entirely suitable for quantity production. An inexpensive, easy to manufacture manifold is desired.